Knowing the longitudinal acceleration of a vehicle as accurately as possible is important for a plurality of vehicle control systems, in particular for systems designed for optimizing the travel dynamics of the vehicle. Such systems are, for example, anti-lock or traction control systems, designed to counter any tendency to lock-up or excessive drive slippage. Dynamics control systems are also known for controlling the transversal movements or yaw of the vehicle. In addition, the vehicle acceleration can also be used for chassis or steering control systems.
FIG. 1, illustrating the conventional method for determining acceleration, is explained briefly below. In general, the longitudinal speed V.sub.1 of the vehicle is measured for this purpose (block 101), for example, in the known manner by analyzing the wheel speed values acquired by sensors. The longitudinal acceleration a.sub.1 of the vehicle is obtained from the longitudinal speed V.sub.1 by differentiation or, in the case of discrete time intervals, subtraction (Block 102). Since signal V.sub.1 representing the longitudinal speed of the vehicle may be affected by interference, the acceleration signal a.sub.1 thus obtained can be filtered in a first- or second-order filter 103. The output signal a.sub.1f present at filter 103 represents then the corrected vehicle acceleration, which is sent to one or a plurality of the aforementioned vehicle control system(s) 104. Correction filtering 103 must be designed so that even strong interference affecting signal V.sub.1 and thus signal a.sub.1 is removed; however, strong filtering can also mean a strong phase shift of signal a.sub.1F in relation to signal a.sub.1, which may cause problems in the subsequent processing in block 104.
Furthermore, it is also known from the related art (e.g., from WO 90/11213), that the instantaneous braking torque, in particular the changes in the braking torque, can be determined, for example, from the estimated wheel brake pressures.
An object of the present invention is to generate an acceleration signal that is as free of distortion as possible in a simple manner.